Radon
Is radon a problem in Colorado mountain homes?
Radon runs high across Colorado's mountain counties, and the only number that counts is the test in the house you are buying.
A live person answers. Not a robot, not a phone tree. Updated September 2026.
Photos: Ski lift climbing the mountain with snowy peaks, morning light, Live Kaiah (Unsplash).
Yes. 50.3% of 30,229 Jefferson County radon tests from 2005 to 2025 came in at or above the EPA action level of 4 pCi/L, per CDPHE data. Park County came in at 49.0% and Summit County at 46.1%, and CDPHE puts mitigation at $1,000 to $2,000.
50.3% at 4 pCi/L or higher.
30,229 CDPHE tests, 2005 to 2025, median 4 pCi/L.
49.0% at 4 pCi/L or higher.
1,064 tests, median 3.8 pCi/L.
$1,000 to $2,000.
CDPHE's range for a mitigation system.
Required since August 7, 2023.
SB23-206 puts a radon warning in every Colorado home sale contract.
How high is radon in Colorado's mountain counties?
- Jefferson County: 50.3%. Of 30,229 pre-mitigation tests from 2005 to 2025, 50.3% came in at or above 4 pCi/L. The median was 4 pCi/L.
- Park County: 49.0%. Of 1,064 tests, 49.0% came in at or above 4 pCi/L, with a 3.8 pCi/L median.
- Summit County: 46.1%. Of 3,724 tests, 46.1% came in at or above 4 pCi/L, with a 3.4 pCi/L median.
- Statewide: 46.4%. Jefferson County runs 3.9 points above the Colorado average.
- 500 deaths a year. CDPHE attributes 500 lung cancer deaths in Colorado each year to radon.
Two houses on the same street test differently. The only number that counts is the test in that house.
What radon level needs fixing?
- 4 pCi/L or higher: fix it. That is the EPA action level.
- A professional test runs $150. CDPHE's figure for a professional radon test.
- Test during the inspection period. Schedule the radon test with the home inspection so results land before the inspection deadline.
What does Colorado radon law require in a home sale?
- SB23-206. Signed June 5, 2023, and in effect August 7, 2023.
- What the contract must include. A radon warning, any known radon test results and mitigation history, and the CDPHE radon brochure.
- Rentals are covered too. Landlords give tenants the same disclosures. A tenant can void a lease when the landlord skips the disclosure or leaves elevated radon unmitigated.
- The lease rule changed in 2026. After January 1, 2026, the tenant's right to void applies only to leases longer than one year.
This states the published rule. A Colorado real estate attorney answers questions on a specific contract or lease.
What does radon mitigation cost in Colorado?
- $1,000 to $2,000. CDPHE's range for a mitigation system.
- Ask for the paperwork. Get the installer's records and the last post-mitigation test from the seller.
- Retest after install. A post-mitigation test shows the system brought the level down.
Questions on a mountain home's radon results? Call the Kenna Real Estate Group at 303-955-4220.
Questions
Quick answers.
Is radon a problem in Colorado?
Yes. Statewide, 46.4% of CDPHE pre-mitigation tests from 2005 to 2025 came in at or above 4 pCi/L.
Is Jefferson County high in radon?
Yes. 50.3% of 30,229 tests came in at or above 4 pCi/L, with a median of 4 pCi/L.
Does Colorado require radon disclosure?
Yes. Since August 7, 2023, SB23-206 requires a radon warning, known test results, mitigation history and the CDPHE brochure in home sale contracts.
How much is radon mitigation in Colorado?
CDPHE puts it at $1,000 to $2,000.
What radon level is too high?
The EPA action level is 4 pCi/L.
Sources
- Jefferson County radon data
- Park County radon data
- Summit County radon data
- CDPHE radon
- CDPHE: testing your home
- Colorado SB23-206
Rules, rates and dates change. The county, town or state office named above has the current version.
Go deeper
Where to go next.
The map
Where the mountain towns are.
Every pin opens that town's page. Drive times from downtown Denver, without traffic.
- Front Range foothills
- I-70 corridor
- Peak to Peak
- Summit County
- Resort
- Tap a town to open its page
Outline: U.S. Census Bureau. Roads from downtown Denver: OSRM on OpenStreetMap. Town points: OpenStreetMap and USGS. Drive times without traffic.
Private consultation
Ask us about your mountain home.
303-955-4220A live person answers. Not a robot, not a phone tree.
- Every mountain town. Evergreen and Conifer to Summit County and Steamboat.
- Wildfire, water, winter. Insurance, well, septic and access checked before you offer.
- One point of contact. From the first call to the closing table.
Colorado Mountain Home Finder is part of the Kenna Real Estate Group at Keller Williams DTC (KWDTC).